Compressor



Sept. 23, 1958 H. D611 2,853,229

COMPRESSOR Filed Nov. 18, 1955 lnven/o I? in HM QJ/z r WMK United States 2,853,229 Patented Sept. 23, 1958 tice COIVIPRESSOR Heinrich Diilz, Stuttgart-Mohringen, Germany, assiguor to Sofix A. G., Vaduz, Liechtenstein, a corporation of Liechtenstein Application November 18, 1953, Serial No. 392,835 Claims priority, application Germany November 24, 1952 Claims. (Cl. 230-200) an electromagnetic or electrodynamic oscillating drive.

With such oscillatory drives, the stroke is subject to certain variations because the movement of the piston is not guided in a fixed path as with a crank drive. In order to keep the stroke uniform, it has been necessary to provide complicated electrical control devices. Mechanical means for limiting the piston stroke have also been proposed, such as a brake to be applied to the piston to forcibly maintain uniformity of the stroke.

With small refrigeration machines, it has been the usual practice to have the compressor piston overtravel the exhaust ports so that a residual gas cushion remains in the cylinder space, which cushion limits the stroke due to its pneumatic buffer action. Such an arrangement to keep the stroke uniform brings about inconstant motion and has the further disadvantage that the cushion of residual gas involves a considerable detrimental space,

which disadvantage so far practically prevented the use of oscillating drives for compressors of small refrigerating umts. The same detrimental effect is observed whether the gas cushion is located within or outside the cylinder, or whether a mechanical buffer, such as elastic material, for instance, rubber, is used. The efiec't of such devices can readily be seen from the consideration that with a .tietrimental space of 8% which is about the minimum necessary for limiting the stroke, and with the usual compression ratio of 1:7, the volumetric efiiciency is reduced to approximately 0.4, that is, the refrigerating effect of such a machine is only 40% of the theoretical value.

The prime object of my invention is to generally improve piston compressors.

in aiming at a piston compressor driven by an oscillating drive, one of the objects of my invention is to ensure a greater freedom as to the end positions of the piston movements. While, due to the use of an oscillating drive, the piston movements will continue not to be accurately limitable, it is no longer of critical importance that definite end positions are reached.

One object of my present invention is to do away with such detrimental cylinder spaces as have been referred .to and to avoid the loss of efficiency associated with :such spaces.

Another object of this invention, particularly when .applied to compressors the piston of which is directly :connected to an induction coil, is to provide means to improve the filling of the cylinder and the action during compression.

least to theendofthe compression space and under usual operating conditions even beyond this space. The top of the compression space is closed by a spring-loaded member which covers the entire cylinder section. Generally, this member is a disc to serve as an exhaust valve so that the piston may easily move beyond the end of the compression space against the force of a relatively weak spring bearing against the member on top of the compression space.

The specification is accompanied by a drawing of which:

Fig. 1 is a partly sectioned elevation of a compressor embodying features of my invention; and

Fig. 2 is a section taken in elevation through a modified part of the compressor, the left-hand and right-hand halves of the view illustrating diiferent details. I

Referring to the drawing, and initially to Fig. l, a circular permanent magnet 1 is provided with an air gap 2 in which a coil 3 is longitudinally movable. The winding 4 of coil 3 is mounted on a body 5 which is electrically and magnetically insulated. The winding 4 is connected to a source 6 of electric current, such as an alternating current line, which causes the coil to move longitudinally within the air gap 2. The coil 3 is connected with a piston rod 7 which preferably forms an integral part .of the compressor piston 8. The piston rod 7 may be additionally supported in a housing member 9 which at the same time may formthe compressor cylinder.

The upper closure of the compressor cylinder 10 is constituted by a spring-loaded member, such as the disc 11, which covers the entire cylinder section. The disc 11 may be returned to its normal position by suitable means, such as a coil spring 12.

The disc 11 is supported in a chamber 13 for free movements and is provided with projections 14 for guiding purposes.

The chamber 13 which is adjacent to the cylinder 10 is enclosed by a special housing 15 which forms the cylinder cover much'in the manner of a cylinder head. It is possible to provide within the housing 15 a second compensation chamber 16 which may surround the first or adjacent chamber 13 at least partly. The second compensation chamber communicates with the first chamber by means of special throttling members 17 which may be circular holes. This arrangement permits the compressed refrigerant to leave the compensation chamber 16 through the exhaust opening 18 practically without impacts, which is particularly important for small compressors for refrigeration units since an impacting release of the refrigerant from the compressor can easily lead to vibrations in the connected pipe system, which, in turn, may result in a bothersome noise and may also have other objectionable eifects.

The disc 11 which acts as an exhaust valve is preferably shaped to have a surface parallel to that of the front or cross section of the cylinder. The two contacting surfaces may actually be ground for best contact. If a direct metallic contact is not desirable, it is possible to provide the contact area of the disc 11 or the front face of the cylinder with an elastic cover.

If the cylinder 10 is provided with special intake openings, such as intake valves, the piston head may be covered with an elastic material 21, which cover may also be provided as an insert for the disc 11, to avoid direct metallic contact.

When the piston is made to oscillate by means of the coil 3 with a stroke that is equal to, or greater than, the length of the cylinder, then with increasing compression and depending on the counter pressure in the chamber 13 the disc 11 will begin to lift even before the piston reaches its top position and will open the cylinder over its entire section. Accordingly, it is possible, for instance, by means of a piston made to oscillate freely by an electric oscillating drive, to operate without sharply defined limits of the stroke, which affords a great simplification of the electric oscillating drive. To maintain the condition of oscillation, the electric oscillating drive may be provided with a spring 19.

As further shown in Fig. l, the intake is arranged so that the compressor cylinder is filled in a known manner through the hollow piston 8. For this purpose, a valve is fitted into the piston head, such as, for example, the poppet valve 20, the surface of which may be covered with an elastic coating 21.

In order to improve the filling of the cylinder and to ensure supercharging, it is further possible to provide the lower end of the piston rod with a shoulder 22 which is reciprocatingly received in a recess 23. This recess may be machined into the magnet 1 so that during the downward stroke of the piston 8 the air volume contained in the recess 23 will be pushed by the shoulder 22 into the cylinder 10, thus effecting a certain amount of supercharging.

It is also possible to have the shoulder 22 operate like a piston in conjunction with the recess 23 so that at this place a considerable amount of supercharging may be achieved. A further bearing for the piston rod may be provided where the piston-like lower end of the rod is received in the recess 23. For the intake to the space between the shoulder 22 and the recess 23, special channels or perforations may be provided so that additional valves need not be resorted to, as is partially indicated in Fig. 2.

In the modification of Fig. 2, the cup-shaped light piston 22' of greater diameter is mounted on a piston rod 7 to operate in a cylinder 23 and to secure supercharging. The cup-shaped piston may be mounted with a sliding fit or in association with the screw member 25 which supports thecoil carrier 5. The cylinder 23' may be provided with special intake valves (not shown) or with intake channels 29.

To achieve perfect guiding of the piston 22, it is mounted on the piston rod 7 so that it will automatically adjust its position at least within narrow limits in a radial direction. In the suspension shown, the piston 22' proper is separated from its mounting 26 by an elastic intermediate member 27. The parts 22 and 26 are joined to the elastic member 27 preferably by an adhesive. The contact areas as shown in Fig. 2 are preferably designed so as to permit movements of the member 22' in a radial direction, while maintaining a greater stiffness in an axial direction. The cross section of the elastic member 27 may increase or decrease radially outwardly or inwardly as indicated in the right-hand half of Fig. 2. This will also help to compensate for slight misalignments.

It is believed that my invention and the construction and operation of the above explained form of apparatus for practicing the invention, and the many advantages thereof, will be fully understood from the foregoing'description. Some of the features of the invention are reviewed hereinafter.

The spring and the spring-loaded member are designed so that even at the greatest possible piston stroke the member after contacting the piston head, will remain on top of the piston head and will return to its position on top of the cylinder when the piston makes its return trip. This can be ensured by two measures which have to be applied jointly. The springconstant and a pretension of the spring have to be such that even at the greatest possible stroke the spring force will always remain greater than the forcedue to the acceleration of the spring-loaded member. Further, the natural frequency of the system consisting of spring and spring-loaded member has to be twice as great as, or greater than twice, the number of strokes.

Thus, it is possible to expel the entire fluid contained in the cylinder and to reduce the detrimental space to 4 practically zero. The output efficiency of such a compressor is, therefore, constant over a wide load range.

It is an advantage of the compressor according to my invention, whereby the piston due to the use of an oscillating drive is not limited to a predetermined path, that the drive can be greatly simplified as far as the free play in the extreme positions of the piston movements is concerned.

The intake for the compressor may take place through a hollow piston rod. In accordance with one feature of my invention, the piston rod extends to form a special shoulder which is reciprocatingly received in a stationary recess so that on the intake stroke of the piston the volume of air within the recess inwardly of the shoulder is somewhat compressed before it reaches the cylinder proper through the piston rod. It is also possible to have the shoulder serve at the same time as a guide for the compressor drive, that is, as a second bearing. It is further possible to provide the shoulder and recess as a piston and cylinder mechanism to act as a true supercharging device, which requires either additional valves or channels or perforations to fill the recess, to be opened by the shoulder in its top position.

It will be apparent that while I have shown and described my invention with respect to one form only, many changes and modifications may be made without departing from the spirit of the invention defined in the following claims.

I claim:

1. A piston-type compressor for small refrigerating machines comprising a cylinder open at one end, a piston reciprocable in said cylinder, a hollow piston rod extending from said piston and reciprocated by electro-magnetic means so that at the end of the stroke in the direction toward said open end of the cylinder said piston at least reaches to said open end of the cylinder, a movable closure for said open end of the cylinder including a disc covering said open end and adapted also to act as an exhaust valve controlling the discharge of compressed gas from the cylinder, a spring acting against said disc and yieldably urging the latter axially against said open end of the cylinder and to a concentric position with respect to the latter, a cylinder head on said open end of the cylinder and defining a first chamber in which said disc is freely movable both axially and radially to accept gas discharged from the cylinder and a second chamber at least in part surrounding said first chamber, said cylinder head'having restricted throttling passages extending between said first and second chambers so that the pressure tends to be equalized in said second chamber, said second chamber having an outlet for compressed gas extending therefrom, and means defining an inlet for gas to be compressed through said hollow piston rod, the spring constant and the prestressing of said spring acting on the disc valve being such that the force exerted by the spring is always greater than the force due to acceleration of said disc valve when the piston is at the limit of its stroke in the direction toward said open end of the cylinder and the natural frequency of said disc valve and related spring is at least twice as high as the frequency at which said piston is reciprocated. Y 2. A piston-type compressor for small refrigerating machines comprising a cylinder open'at one end, a piston reciprocable in said cylinder, electro-magnetic means reciprocatingsaid piston in a variable range within the cylinder depending on the load, but which, under all loads, causes said piston to reach at least to said open end of the cylinder at the end of the stroke of the piston toward said open end, a movable closure for said open end of the cylinder including a disc extending across said open end of the cylinder and adapted also to act as an exhaust valve controlling the discharge of compressed gas from the cylinder, said disc being freely movable both axially and radially with respect to said cylinder, anda spring acting against said disc and yieldably urging the latter axially against said open end of the cylinder and to a position concentric with respect to the latter, said spring having a spring constant and being prestressed to provide a'force acting against said disc valve that is always greater than the force due to acceleration of said disc valve when the piston is at the limit of its stroke in the direction toward said open end of the cylinder, and said spring and disc valve having a natural frequency that is at least twice as high as the frequency at which said piston is reciprocated.

3. A piston-type compressor for small refrigerating machines comprising a cylinder open at one end, a piston reciprocable in said cylinder, a hollow piston rod extending from said piston and reciprocated by electromagnetic means so that at the end of the stroke in the direction toward said open end of the cylinder said piston at least reaches to said open end, a disc valve covering said open end of the cylinder and being movable away from the latter to permit exhaust of compressed gas from the cylinder, a spring acting against said disc valve and urging the latter to a seated position against said open end of the cylinder, a cylinder head on said open end of the cylinder and defining a first chamber receiving said disc valve to accept gas discharged from the cylinder and a second chamber at least in part surrounding said first chamber, said cylinder head having restricted passages extending between said first and second chambers so that the pressure tends to be equalized in said second chamber, said second chamber having an outlet for compressed gas extending therefrom, the interior of said hollow piston rod opening into said cylinder to define an inlet for the gas to be compressed, an inlet valve associated with said inlet for the gas to be compressed, a fixed member having a recess therein defining a supercharging cylinder receiving the end of said piston and receiving the gas to be compressed, a cup-shaped member on said remote end of the piston rod and fitting closely within said recess to define .a supercharging piston so that, during the stroke of said rod in the direction away from said open end of the first mentioned cylinder, gas in said supercharging cylinder is compressed and fed through said inlet into the first mentioned cylinder, and said fixed member having gas inlet passages opening into said recess at locations which are exposed when said rod is at the limit of its stroke in said direction toward the open end of the first mentioned cylinder.

4. A piston-type compressor for small refrigerating machines comprising a cylinder open at one end, a piston reciprocable in said cylinder, a hollow piston rod extending from said piston and reciprocated by electromagnetic means so that at the end of the stroke in the direction toward said open end of the cylinder said piston at least reaches to said open end, a disc valve covering said open end of the cylinder and being movable away from the latter to permit exhaust of compressed gas from the cylinder, a spring acting against said disc valve and urging the latter to a seated position against said open end of the cylinder, a cylinder head on said open end of the cylinder and defining a first chamber receiving said disc valve to accept gas discharged from the cylinder and a second chamber at least in part surrounding said first chamber, said cylinder head having restricted passages extending between said first and second chambers so that the pressure tends to be equalized in said second chamber, said second chamber having an outlet for compressed gas extending therefrom, the interior of said hollow piston rod opening into said cylinder to define an inlet for the gas to be compressed, an inlet valve associated with said inlet for the gas to be compressed, a fixed member having a recess therein defining a supercharging cylinder receiving the end of said piston rod remote from said piston and receiving the gas to be compressed, a cup-shaped member on said remote end of the piston rod and fitting closely within said recess to define a supercharging piston so that, during the stroke of said rod in the direction away from said open end of the first mentioned cylinder, gas in said supercharging cylinder is compressed and fed through said inlet into the first mentioned cylinder, and means elastically yieldable at least in the radial direction and mounting said cup-shaped member on said piston rod.

5. A piston-type compressor according to claim 4; wherein said means mounting the cup-shaped member on the piston rod includes a generally radial flange on said rod, and an elastic ring adhesively secured between said radial flange and a confronting radial bottom surface of said cup-shaped member.

References Cited in the file of this patent UNITED STATES PATENTS 855,050 Dietrich May 28, 1907 2,251,490 Kucher Aug. 5, 1941 FOREIGN PATENTS 19,425 Great Britain of 1898 506,623 France Aug. 26, 1920 

